Normally, a 2m high tide at our place goes to the top of our boat ramp and is an hour later than the Fort Denison prediction. Sometimes we get a high tide that comes well over our boat ramp and up onto the grass. We have had a few when we were literally paddling in water.
I know that weather can have an impact on the height of the tide. Our January east coast low provided a good example. I took the first picture below at high tide on 18 January, 2025. It was a predicted 1.67m tide. I then compared the photo to the tides over the next few weeks. The third and fourth photos show the water at a similar level. These were both 1.9m plus tides over a week later. I marked a stick at 0.1m intervals to get an idea of the levels. The East coast low resulted in a water level that was about 0.3m higher than normal (the height of a ruler).
In fact, the opposite is also true. If we have a high pressure system, it reduces the height of the tide- see photo 7. The influence of pressure on the height of the high tide is about 0.5m from large high pressure systems to east coast lows and even more for areas near the eye of a cyclone (really big low pressure systems). Cyclones also generate large wind driven waves, increasing their impact.
This makes it very hard to see the impact of climate change on sea level. In NSW we have a tidal range of about 2m and on top of that, we have a weather variability of plus or minus roughly 0.3m. Currently sea level is rising at about 0.01 to 0.02cm per year, making it very hard to notice in the short term. However, over a period of 10 years, this is getting to within the range of the natural variablility. Within 100 years it will be very noticeable, because unlike humans, our buildings and structures have very long memories. Even if we limit global warming to 1.5 degrees (which seems highly unlikely), sea level rise is predicted to accelerate and will be more than 2m in the next century. A rise of 6m plus is more likely. We may not yet be noticing the rise due to the sheer natural variabiliy in the system, but the Pacific Islander people are already feeling the impacts with contamination of their water tables with salty sea water and inundation of their foreshores.
Watch out for a late autumn high tide on May 27 and 28, which is predicted to be 2.11m around midnight. Let’s hope this does not coincide with a strong low pressure system.
1. January 18, 2025 at 12.56pm. High tide predicted at 1.01pm of 1.67m
2. January 28, 2025 at 10.27am. Tide predicted to be about 1.67m at this time.
3. January 30 2025 at 10.57am. High tide of 1.95m at 10.43am
4. January 31, at 11.50am. High tide predicted at 11.26am of 1.97m.
5. February 1, 2025 at 12.02pm. High tide predicted at 12.10pm of 1.93m
6. High tide of 2.04m on 2 January 2018. Our boat ramp was submerged.
7. High tide on 10 February 2025 at 8.55am under the influence of a high pressure system. Predicted high tide was 1.80m at 8.36am. Notice the difference between the water level in this photo compared to photo 1.
